The present invention relates to the field of semiconductor integrated circuits and, in particular, to a novel method for forming high quality rhodium (Rh) films.
Thin film technology in the semiconductor industry requires thin deposition layers, increased step coverage, large production yields, and high productivity, as well as sophisticated technology and equipment for coating substrates used in the fabrication of various devices. For example, process control and uniform film deposition directly affect packing densities for memories that are available on a single chip or device. Thus, the decreasing dimensions of devices and the increasing density of integration in microelectronics circuits require greater uniformity and process control with respect to layer thickness.
Various methods for depositing thin films of complex compounds, such as metal oxides, ferroelectrics or superconductors, are known in the art. Current technologies include mainly RF sputtering, spin coating processes, and chemical vapor deposition (CVD), with its well-known variation called rapid thermal chemical vapor deposition (RTCVD). These technologies, however, have some disadvantages. For example, the RF sputtering process yields poor conformality, while the spin deposition of thin films is a complex process, which generally involves two steps: an initial step of spinning a stabilized liquid source on a substrate usually performed in an open environment, which undesirably allows the liquid to absorb impurities and moisture from the environment; and a second drying step, during which evaporation of organic precursors from the liquid may leave damaging pores or holes in the thin film. Further, both CVD and RTCVD are flux-dependent processes requiring uniform substrate temperatures and uniform distribution of the chemical species in the process chamber.
Promising candidates for materials for capacitor electrodes in IC memory structures include noble metals, such as platinum (Pt), palladium (Pd), iridium (Ir), ruthenium (Ru), rhodium (Rh) and osmium (Os), as wells as their conductive oxides (for example, ruthenium oxide (RuO2), iridium oxide (IrO2) or osmium oxide (OSO2), among others). Although the above-mentioned noble metals are all physically and chemically similar, platinum (Pt) is most commonly used because platinum has a very low reactivity and a high work function that reduces the leakage current in a capacitor. Platinum is also inert to oxidation, thus preventing oxidation of electrodes which would further decrease the capacitance of storage capacitors. The use of platinum as the material of choice for capacitor electrodes poses, however, problems. One of them arises from the difficulty of etching and/or polishing platinum.
Recently, particular attention has been accorded to rhodium (Rh) as an alternative material to platinum because rhodium has excellent electrical properties which are the result of good electrical conductivity, good conductivity, good heat-transfer properties and high work function. Rhodium films are currently deposited by sputtering, CVD or RTCVD, among others. Although the CVD processing technologies afford good step coverage, as the geometries of the future generations of semiconductors become extremely aggressive, these processing technologies will not be able to afford better step coverage, that is a high degree of thickness and/or uniformity control over a complex topology for thin films of such future generation of semiconductors.
Accordingly, there is a need for an improved carbon-free rhodium film with good step coverage and improved electrical properties, as well as a new and improved method for forming such continuous and smooth rhodium films with good step coverage.
The present invention provides a novel method for the formation of rhodium films with good step coverage which may be used as top and/or lower plate electrodes for a capacitor. Rhodium films are formed by a low temperature atomic layer deposition technique using a rhodium gas precursor followed by an oxygen exposure. The invention provides, therefore, a method for forming smooth and continuous rhodium films which also have good step coverage.